1. Field of the Invention
The present invention relates to a light emitting device, and more particularly relates to light emitting device which has an excitation light source, a wavelength converting member, and a light guide.
2. Background Information
Conventionally, endoscope devices for in vivo observations and for performing treatment during observations, and fiber scopes for observing in extremely narrow or extremely dark spaces have been widely used.
Endoscopes and fiber scopes are constructed with extremely minute light guides and are able to illuminate spaces or the like such as inside body cavities like the stomach or other gaps or the like because the fibers transfer light which has been radiated from a light source.
In order to efficiently illuminate using minute fibers, the light source must be very bright. Furthermore, when observing and in some cases diagnosing an affected area of an organ or within cavities, accurate reproduction of color information is necessary. Thus, the light source for endoscopes and fiber scopes must provide light which is close to natural light.
Therefore, the use of semiconductor light emitting elements such as light emitting diode elements (LED) and laser diode elements (LD) or the like have been proposed as light sources to replace xenon lamps or the like (for instance, JP 2002-95634-A).
Furthermore, an illuminating device which uses semiconductor light emitting elements has been proposed (for instance, JP 2003-515899-A).
Semiconductor light emitting elements are compact, have good power efficiency, and emit brilliant colored light. Furthermore, these elements are formed from semiconductors, so there is no concern that the elements will burn out. In particular, semiconductor lasers emit light which has extremely high intensity compared to that of light emitting diodes, and therefore can realize light sources with excellent illumination.
In recent years, semiconductor lasers which emit blue wavelength light have been developed, and the light emitting efficiency thereof is extremely high. Therefore, various illuminating devices and light emitting devices which use semiconductor lasers as light sources for achieving RGB light have been proposed. These devices have been able to overcome conventional issues, such as failure to achieve sufficient light emitting efficiency and brightness, by using wavelength converting members which emit blue light.
However, as described above, when using an endoscope or the like, a device with excellent color rendering properties is required. Furthermore, excellent color rendering properties are also required of illuminating devices for automotive applications in order to distinguish people and signs.
In particular, sufficient color rendering properties cannot be sufficiently achieved when using a semiconductor laser which emits blue wavelength light because of the unique properties of this laser, namely the property of having a linear spectrum in the blue wavelength band and having extremely low light emitting intensity across a relatively wide band of adjacent wavelength bands (such as near ultraviolet bands and blue-green wavelength bands).
In addition, extremely high brightness may be required depending on the use of the light source device, but there is a mutual trade-off relationship between light emitting efficiency/brightness and color rendering properties, and sufficiently achieving satisfactory levels of both light emitting efficiency and color rendering properties is difficult.
Note that semiconductor light emitting elements such as semiconductor lasers are required to have even higher brightness and high light emitting efficiency, but the light density is generally high, so the resins and the fluorescent material or the like which make up the wavelength converting member will be heated and degraded by the high density excitation light, thus leading to a shorter life for the light emitting device.